Importance of functional biodiversity and species-specific traits of benthic fauna for ecosystem functions in marine sediment

Fauna have been found to regulate important biogeochemical properties and ecosystem functions in benthic environments. In this study, we focused on how functional biodiversity and species-specific traits of benthic macrofauna affect key ecosystem functions related to organic matter mineralization and cycling of nutrients in surface sediments. Dominant benthic invertebrates from the Baltic Sea and the Skagerrak were classified into functional groups in accordance with their behaviour, feeding and sediment reworking activities. Macrofauna species were added in different combinations to defaunated Baltic sediments in 2 parallel microcosm systems fuelled with brackish and marine water. In total, there were 12 treatments that differed in terms of functional diversity of benthic fauna. The experiments demonstrated that faunal activities directly affected benthic oxygen and nutrient fluxes, sediment reactivity and pore-water distribution under both Baltic and Skagerrak conditions. Benthic fluxes, sediment reactivity and pore-water distribution were similar in Baltic and Skagerrak treatments, in which the same functional biodiversity and species-specific traits of benthic macrofauna were observed. Although no significant effects of functional biodiversity could be detected under Baltic or Skagerrak conditions, treatments with bioturbating fauna from the Skager- rak enhanced oxygen consumption and nutrient fluxes compared to treatments with Baltic fauna and Skagerrak fauna with functional groups similar (parallel) to the Baltic fauna. Moreover, species- specific traits related to the Skagerrak fauna (e.g. the thalassinid shrimp Calocaris macandreae) exceeded the effects of all other faunal treatments. This suggests that species-specific traits of macro- fauna may override species richness and functional biodiversity of macrofauna when regulating important ecosystem properties and functions in benthic environments.